Conventionally, in spaces for production and residence such as a plant and a building, an incinerator like a boiler is used. Such an incinerator burns fuel. In this time, if being contained in the fuel, the sulfur component is exhausted as sulphur dioxide (SO2) gas without being fixed in ash. The sulphur dioxide gas is showered on the ground as acid rain and affects a human body, an animal, and natural environment. Generally, the incinerator is provided with an exhaust gas desulfurization apparatus not to affect adverse influence.
Most of the exhaust gas desulfurization apparatuses installed in the large-sized combustion facilities are a wet type. In the wet type exhaust gas desulfurization apparatus, the exhaust gas is made to contact alkaline absorption liquid like limewater and the sulphur dioxide gas is changed into sulfite. In this way, the sulfite is absorbed in the absorption liquid and is removed. Moreover, the sulfite is oxidized with air and is changed into sulfate. For the oxidation reaction, generally, the technique is adopted in which air is spouted into the absorption liquid.
In the technique in which the air is spouted into the absorption liquid, it is demanded to make the oxidation reaction effective. Therefore, various kinds of techniques are conventionally developed.
FIG. 1 shows a first conventional example of the wet type exhaust gas desulfurization apparatus. The first conventional example of the wet type exhaust gas desulfurization apparatus 101 is provided with an absorption tower 102 which carries out a wet type desulfurization, and a liquid reservoir 103 is arranged below the absorption tower 102 to reserve alkaline absorption liquid b. Alkali absorbent a such as lime is introduced into the absorption liquid b. The absorption liquid b is pumped up into the absorption tower 102 through a pipe 105 by a circulation pump 104 and is sprayed by spray pipes 106. Combustion exhaust gas d is introduced from the top of the absorption tower 102, contacts the sprayed alkali absorption liquid b. Thus, sulphur dioxide gas in the exhaust gas reacts with the alkaline absorbent and is changed into sulfite. The sulfite is absorbed by the absorption liquid and falls into the liquid reservoir 103 and is collected therein. Air d is spouted into the absorption liquid a containing the sulfite by a blower 107. The blower 107 is connected with a plurality of nozzle headers 108 which are arranged in the bottom of the liquid reservoir 103. The air is spouted into the absorption liquid b from a discharge port 110 provided at the tip of an air supply nozzle 109 extending from each nozzle header 108. The sulfite in the absorption liquid b reacts with the spouted air and is changes to sulfate. The sulfate stoichiometrically equivalent to the sulphur dioxide absorbed in the absorption liquid b is discharged as waste fluid c. Absorption efficiency in the oxidation technique by the above air blowing method is mainly influenced based on the contact area between air and the absorption liquid.
FIG. 2 shows a second conventional example of the wet type exhaust gas desulfurization apparatus 111. In the second conventional example, the wet type exhaust gas desulfurization apparatus 111 is composed of stirrer 112. The stirrer 112 has stirring wings 113, and the stirring wings 113 are rotated in the absorption liquid of the liquid reservoir 103. The air is supplied by a blower 107 and spouted into the absorption liquid b from a discharge port 114 arranged in the front of the stirring wings 113. The spouted air accompanies a spouted stream generated by the stirring wing 113 and is distributed into the absorption liquid b. This technique can promote the oxidation reaction by the distribution of air.
Japanese Laid Open Utility Model Application (JP-A-Heisei 4-137731) shows a third conventional example of the wet type exhaust gas desulfurization apparatus 121 shown in FIG. 3. A plurality ofjet nozzles 117 are provided to generate jet streams 116 in a predetermined angle into the radial directions of the liquid reservoir 115. The plurality of jet streams 116 are provided at a predetermined height, and the jet stream from the jet nozzle 117 turns to the circumferential direction of the liquid reservoir 115. An absorption liquid pipe 119 is arranged in the bottom of the jet nozzle 117 to pass through the liquid reservoir 115, and a jet stream pump 118 is provided on the way of the pipe 119. The opening of an air supply pipe 120 is provided on the way of the absorption liquid pipe 119. Air f is sucked from the air supply pipe 120 by the absorption liquid flowing though the absorption liquid pipe 119 and is spouted into the liquid reservoir 115 from the jet nozzles 117 together with the absorption liquid b. This technique can promote the mixing of the absorption liquid and the air more.
FIG. 4A shows a fourth conventional example of the wet type exhaust gas desulfurization apparatus 131. A discharge pipe 122 penetrates the circumferential wall of the liquid reservoir 123. Absorption liquid is sucked from a liquid reservoir 123 by a liquid pump 124 and circulated through a circulation liquid pipe 125 and a discharge pipe 122. As shown in FIG. 4B, the end of the air blow pipe 126 is inserted into the circulation liquid pipe 125 on the way of circulation liquid pipe 125. The direction 127 of an air output portion 126a of the air blow pipe 126 is almost coincident with the flowing direction of the absorption liquid in the circulation liquid pipe 125. The air is pressurized by a blower 128 and is outputted from the end of the air blow pipe 126 into the direction 127. Tn this way, the air is mixed with the absorption liquid b in the circulation liquid pipe 125 and is spouted from a discharge pipe 122 in the absorption liquid in the liquid reservoir 123.
The first to fourth conventional examples are superior in the oxidation promotion but the following problems are remained.
In the first conventional example, a checking work of the liquid reservoir 103 is troublesome, because a lot of air supply nozzles 109 are arranged on the whole bottom surface of the liquid reservoir 103.
In the second conventional example, the rising stream is generated due to air lift operation which accompanies the spouting of the air from the discharge port 114. The rising stream promotes a narrow region circulation in which the stirring wing 113 absorbs and stirs a part of the liquid again. As a result, the outreach of the stirred liquid stream becomes short and the stirring efficiency decreases.
In the third and fourth conventional examples, air is supplied from the way of the jet nozzle 117 which is connected with absorption liquid pipe 119 or the discharge pipe 122 which is connected with circulation liquid pipe 125. Therefore, while air bubbles flow through the absorption liquid pipe 119 or circulation liquid pipe 125 together with the liquid, the air bubbles combine and enlarge. As a result, the jet stream is separated into an air phase and an absorption liquid phase. Even if the mixture stream of the air and the liquid is spouted from the jet nozzle 117 or discharge pipe 122 in such a condition, the air bubbles are not uniformly distributed and the perfect oxidation is difficult. Also, the inside of the pipe becomes easy for cavitation erosion.
Therefore, the more increase of the contact area between the liquid and air and the large improvement of the stirring and dispersing capability of the absorption liquid are demanded. Also, it is demanded that the increase and the improvement are achieved in a wide region and uniformly. Furthermore, the large reduction in the number of air supply nozzles and the simplification of the checking work are demanded.